Hemolysis of human or chicken erythrocytes by Sendai virus causes a change in the structure of the erythrocyte membrane
lipid bilayer that can be detected by
spin label electron spin resonance. In the intact erythrocyte, the
phosphatidylcholine derivative
spin label exists in a more rigid environment than the corresponding
phosphatidylethanolamine label. Virus-induced
hemolysis tends to abolish this difference in fluidity, i.e., the region of the
phosphatidylcholine spin label becomes more fluid and that of the
phosphatidylethanolamine spin label becomes more rigid.
Fatty acid derivative
spin labels, which may detect some "average" environment, show no change in fluidity. The fluidity change is detected at several different positions in the fatty acyl chain of the
phosphatidylcholine spin label. Sendai virions grown in Madin-Darby bovine kidney (MDBK) cells or grown in eggs and harvested early, which lack hemolytic activity, cause no significant change in bilayer structure. Hemolytic activity and the ability to alter erythrocyte bilayer fluidity can be activated in MDBK-grown Sendai virions by
trypsin treatment in vitro and in early-harvest egg-grown Sendai virions by freezing and thawing. Erythrocyte ghosts prepared by osmotic
hemolysis and resealed by treatment with Mg2+ or elevated ionic strength exhibit a difference in fluidity between
phosphatidylcholine and
phosphatidylethanolamine spin labels, although less than that observed in whole cells. Incubation of resealed ghosts with Sendai virus abolishes the difference in fluidity. Unsealed ghosts that have been extensively washed show no heterogeneity in membrane bilayer fluidity, and incubation with Sendai virus causes no further fluidity change. Virus-induced
hemolysis as measured by
hemoglobin release is more sensitive to inhibition by Ca2+ than is the associated fluidity change in the bilayer.